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In applied sciences, the equivalent radius (or mean radius) is the radius of a circle or sphere with the same perimeter, area, or volume of a non-circular or non-spherical object. The equivalent diameter (or mean diameter ) ( D {\displaystyle D} ) is twice the equivalent radius.
A sphere of radius r has area element = . This can be found from the volume element in spherical coordinates with r held constant. [9] A sphere of any radius centered at zero is an integral surface of the following differential form: + + =
Plot of the surface-area:volume ratio (SA:V) for a 3-dimensional ball, showing the ratio decline inversely as the radius of the ball increases. A solid sphere or ball is a three-dimensional object, being the solid figure bounded by a sphere. (In geometry, the term sphere properly refers only to the surface, so a sphere thus lacks volume in this ...
Lines, L. (1965), Solid geometry: With Chapters on Space-lattices, Sphere-packs and Crystals, Dover. Reprint of 1935 edition. A problem on page 101 describes the shape formed by a sphere with a cylinder removed as a "napkin ring" and asks for a proof that the volume is the same as that of a sphere with diameter equal to the length of the hole.
Thus, the segment volume equals the sum of three volumes: two right circular cylinders one of radius a and the second of radius b (both of height /) and a sphere of radius /. The curved surface area of the spherical zone—which excludes the top and bottom bases—is given by =.
If one knows that the volume of a cone is (), then one can use Cavalieri's principle to derive the fact that the volume of a sphere is , where is the radius. That is done as follows: Consider a sphere of radius r {\displaystyle r} and a cylinder of radius r {\displaystyle r} and height r {\displaystyle r} .
In Euclidean n-space, an (open) n-ball of radius r and center x is the set of all points of distance less than r from x.A closed n-ball of radius r is the set of all points of distance less than or equal to r away from x.
If, for instance, the area of a sphere is equated to the area of a cube, the equivalent radius is sqrt(3/(2*pi))*a, using the nomenclature on the page. The corresponding SA:V ratio is sqrt(6*pi)/a. If the volume of a sphere is equated to the volume of a cube, the equivalent radius is a times cube root of 3/(4*pi), and the corresponding SA:V is ...